Thin-film magnetic head

ABSTRACT

A thin-film magnetic head which can simultaneously trace two tracks is disclosed. This head comprises: a pair of magnetic gap portions; and a pair of magnetic thin-film layers each of which includes a magnetic pole portion in contact with the magnetic gap portion. A distance between these layers increases as they go away from the magnetic pole portions. Each of the layers includes an expanded portion having a cross sectional area in the passing direction of the magnetic fluxes which is larger than a cross sectional area in the passing direction of the magnetic fluxes at the magnetic pole portion.

This is a division of application Ser. No. 037,070, filed Apr. 13, 1984,which is a continuation of Ser. No. 641,738, filed Aug. 17, 1984, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin-film magnetic head and, moreparticularly, to thin-film magnetic heads which can simultaneously tracetwo tracks.

2. Description of the Prior Art

Recently, as an apparatus for recording and reproducing a still picture,a magnetic recording and reproducing apparatus using a magnetic disk hasbeen proposed.

In such an apparatus, a still video signal of one field is generallyrecorded in one circular track which circles the magnetic disk. However,in the case where the diameter of magnetic disk is small as theapparatus becomes small-sized or the like, such a signal cannot berecorded in one circular track to ensure a sufficient recording density,so that it is necessary to record the still video signal of one field intwo tracks.

In this case, it is obviously desirable to use magnetic heads which cansimultaneously record and reproduce the signal.

On the other hand, in case of recording a still video signal of twofields, i.e., one frame, even in the case where the video signal of onefield is recorded in one circular track and the still picture isrecorded and reproduced by use of two circular tracks, it is desirablethat the magnetic heads can simultaneously trace two tracks.

However, when such magnetic heads which can simultaneously trace twotracks are constructed as conventional bulk types having, ring-likemagnetic cores, there is a large amount of crosstalk between two trackssince a pair of bulk type magnetic cores are extremely closely arranged,so that this causes a practical problem.

Therefore, use is made of thin-film magnetic heads which can beconstituted as extremely small-sized heads as compared with the bulktype magnetic heads.

Thin-film magnetic heads have many advantages such that: they can beformed by various kinds of thin-film depositing methods similar to thesemiconductor manufacturing process; working accuracy is remarkablygood; a plurality of heads can be extremely easily formed on the samesubstrate; mass production is possible; and uniform products can bederived.

Therefore, thin-film magnetic heads are widely used in informationequipment including an external storage device of an electroniccomputer, video tape recorders, magnetic recording camera, etc. as themagnetic recording is performed at a high density.

FIG. 1 shows a conventional structure of conventional thin-film magneticheads.

FIG. 1 illustrates an example of heads which can simultaneously tracetwo tracks and the conductors of which are spirally formed such thatthey are turned three times.

In FIG. 1, a numeral 1 denotes a magnetic substrate and conductors 6 areformed on the magnetic substrate 1 such that they are turned threetimes. Recording currents are supplied to the conductors 6 fromelectrodes 7 also formed on the magnetic substrate 1.

On the other hand, a numeral 4 represents upper magnetic layers whichconsist of magnetic thin films and form the other magnetic yokes asparts of magnetic circuits of the magnetic heads. Respective ends of theupper magnetic layers 4 are fixed to the sides of contact holes 2 formedat central portions of the spiral conductors 6, thereby providing themagnetic junctions with the magnetic substrate 1. The other ends arefixed in the manner such that they face the side of edge portions of themagnetic substrate 1, thereby forming magnetic gaps 5 between the edgeportions of the upper magnetic layers 4 and the edge portions of themagnetic substrate 1.

The respective layers which are formed on and over the magneticsubstrate 1 shown in FIG. 1 are formed by the thin-film depositingmethod and photolithography, respectively.

In FIG. 1, the insulation layers between the respective layers areomitted.

For magnetic recording by use of such thin-film magnetic heads, magneticfields are generated on the sides of magnetic gaps 5 by allowingrecording current to flow through the conductors 6 from the electrodes7, thereby magnetizing a magnetic recording medium (not shown) which islocated near the gap portions. Thus, the magnetic recording isperformed.

On the other hand, for reproducing the signals magnetically recorded,the magnetic fluxes generated form the recorded and magnetized portionson the magnetic recording medium which are located near the magneticgaps 5 pass through the magnetic substrate 1 and upper magnetic layers 4and cross the conductors 6. These magnetic fluxes are changed as themagnetic recording medium is moved, causing voltages to be inducedbetween the conductors 6 and the electrodes 7. Therefore, reproductionis performed by detecting these voltages.

The crosstalk between the tracks occurs due to two reasons: the coils ofthe two tracks have direct magnetic coupling; and the magnetic fluxleaps between the magnetic yokes of the two tracks.

The crosstalk due to the leap of the magnetic flux between the magneticyoke increases as the facing areas of magnetic yokes increase.

On the other hand, in the thin-film magnetic heads, thicknesses ofmagnetic yokes are small and those facing areas can be made remarkablysmaller than those of bulk heads; therefore, a decrease in crosstalk canbe expected.

However, when the thicknesses of upper magnetic layers 4 as the magneticyokes and of the magnetic substrate 1 are reduced, the magneticresistances of the magnetic yoke portions are enlarged, causing adrawback such as deterioration in efficiencies upon recording andreproduction.

To overcome such a drawback, for example, it is necessary to set thewidths in the directions of tracks of upper magnetic layers 4 to belarge. However, when such a structure is adopted, the portion where themagnetic yokes of both tracks approach becomes long, so that crosstalkeasily occurs and cannot be reduced below, e.g., -40 dB.

Namely, since the extraction electrodes extracted from the two heads arealternately formed on the substrate in the same repetitive pattern, theextraction electrodes of the two heads are not symmetric with respect tothe right and left sides and the mutual distributed capacitances are notequal. Thus, there is the drawback that the electromagnetic conversioncharacteristics of the two heads are not balanced.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the drawbacks ofthe conventional thin-film magnetic heads as mentioned above.

Another object of the invention is to provide thin-film magnetic headswhich can reduce the crosstalk between the tracks.

Still another object of the invention is to provide thin-film magneticheads in which the electromagnetic conversion characteristics of twoheads are balanced.

Still another object of the invention is to provide thin-film magneticheads which are resistant to influence by external noise.

To achieve such objects, according to the present invention, there isgiven, as one embodiment thereof, a thin-film magnetic head capable ofsimultaneously tracing two tracks, comprising a pair of magnetic gapportions; and a pair of magnetic thin-film layers each of which includesa magnetic pole portion in contact with said magnetic gap portion, eachof said layers including an expanded portion having a cross sectionalarea in the passing direction of the magnetic fluxes which is largerthan a cross sectional area in the passing direction of the magneticfluxes at said magnetic pole portion, and a distance between saidmagnetic thin-film layers increasing as they go away from said magneticpole portions.

The above and other objects, features and advantages of the presentinvention will be apparent from the following detailed description inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the structure of conventionalthin-film magnetic heads;

FIG. 2 is a plan view showing the shapes of magnetic thin films ofthin-film magnetic heads according to one embodiment of the presentinvention;

FIG. 3 is a plan view showing the shapes of magnetic thin films ofthin-film magnetic heads according to another embodiment of theinvention;

FIG. 4 is a perspective view showing thin-film magnetic heads accordingto still another embodiment of the invention;

FIG. 5 is a perspective view showing thin-film magnetic heads accordingto further another embodiment of the invention;

FIG. 6 is a perspective view showing thin-film magnetic heads accordingto still another embodiment of the invention; and

FIG. 7 is a perspective view showing thin-film magnetic heads accordingto still another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a diagram for explaining an embodiment of the presentinvention, in which magnetic yokes 10 and 10' correspond to the uppermagnetic layers 4 shown in FIG. 1. These magnetic layers 10 and 10' havethe symmetrical shapes with respect to the right and left sides as willbe obvious from FIG. 2.

Assuming that the axis of symmetry is l, rectilinear portions 12 and 12'are formed at the side edges on the side of the axis l of symmetry ofthe respective magnetic yokes 10 and 10' by predetermined distances fromthe sides of magnetic gaps 11 and 11'. Further, arc-like portions 13 and13' are continuously formed from the final end portions of therectilinear portions 12 and 12'.

The arc-like portions 13 and 13' form parts of circles having centers Oand O' and radii of r in the respective magnetic yokes 10 and 10'. Theareas surrounded by the arc-like portions 13 and 13' are approximatelyone-fourth of the area of the circle with the radius of r.

Therefore, the arc-like portions 13 and 13' are formed in the directionsuch as to go away from the axis l of symmetry.

In addition, the arc-like portions 13 and 13', as a whole, form parts ofthe magnetic yokes 10 and 10' which swell in the direction such as to goaway from the axis l of symmetry.

Then, magnetic pole portions 14 and 14' having predetermined widths areformed on the sides of the magnetic gaps 11 and 11' of the respectivemagnetic yokes 10 and 10'.

With such a structure, as the magnetic yokes 10 and 10' go away from thesides of the magnetic gaps 11 and 11', respectively, the distancebetween them increases, thereby preventing the occurrence of thecrosstalk due to approach of the magnetic yokes.

In the case of magnetic yokes 10 and 10' being the magnetic circuits ofthe magnetic heads, the magnetic cross sectional areas are enough forthe magnetic fluxes to pass therethrough, thereby allowing magneticefficiency to be remarkably improved.

Namely, the arc-like expanded portions of the magnetic yokes 10 and 10'coincide with the directions of magnetic fluxes flowing through themagnetic yokes 10 and 10'. Therefore, it is possible to constitute themagnetic heads with good efficiencies in which there is no vain portionsas the magnetic circuits.

In addition, since the magnetic yokes are arranged such that thedistance therebetween increases as they are apart from the sides of themagnetic gaps, the magnetic fluxes which leap to the side of theadjacent magnetic yokes become less, so that the crosstalk extremelydecreases.

Although there have been shown, as an example, the magnetic yokes 10 and10' with the structure whereby the shapes thereof have the expandedportions which, as a whole, have arc-like portions and go away from oneanother, the peripheral edges of the yokes are not always arc-likeshaped. For example, they may be a polygonal shaped.

On the other hand, in the foregoing embodiment, there has been shown anexample whereby the invention was applied to the sides of the uppermagnetic layers constituting one of the magnetic yokes of the magneticheads. However, the invention may be applied to any one of the sides oftwo magnetic yokes which exist so as to sandwich the magnetic gaps.

Also, in the case of forming both magnetic yokes with magnetic films,both magnetic yokes can be formed like the shapes shown in FIG. 2. Withsuch a structure, a further large effect is derived.

FIG. 3 is a diagram for explaining another embodiment of the presentinvention, in which the same and corresponding parts and elements asthose shown in FIG. 2 are designated by the same reference numerals andtheir descriptions are omitted.

In this embodiment, the locations of the centers O and O' of the circlesforming the arc-like portions 13 and 13' are limited.

Practically speaking, when it is assumed that the distances from thebase portions of the magnetic pole portions 14 and 14' to the edgeportions of the respective magnetic yokes 10 and 10' are a and thedistances from the centers O and O' to the edge portions of the magneticyokes 10 and 10' are b, they are set such that the ratio a/b lies withina range of 1.75<a/b<2.25.

With such a structure, as shown by the arrows in FIG. 3, the magneticfluxes passing through the respective magnetic yokes 10 and 10' can beconcentrated to the sides of the magnetic gaps 11 and 11', therebyenabling the magnetic efficiencies to be further increased.

As described above, the magnetic thin films as shown in FIGS. 2 or 3 areused as parts of the magnetic circuits; the two magnetic yokes areadjacently and symmetrically arranged with respect to the right and leftsides in a manner such that the distance between those yokes increasesas they go away from the sides of the magnetic gaps; and the expandedportions having the cross sectional areas where the magnetic fluxes passthrough which are larger than the cross sectional areas of the magneticpole portions are provided. Consequently, the shapes of the magneticyokes can be made substantially coincident with the direction in whichthe magnetic fluxes flow, thereby enabling the magnetic efficiencies tobe remarkably raised. Also, since the distance between the magneticyokes gradually becomes large, the crosstalk extremely decreases.

FIG. 4 is a perspective view for explaining still another embodiment ofthe invention, in which a substrate 21 is formed of magnetic materialsuch as ferrite or the like and constitutes a lower magnetic layer ofthe magnetic heads.

Coils 22 and 22' consisting of the patterns of conductive material whichare wound in the opposite directions are formed on the substrate 21 atsymmetrical locations with regard to the right and left sides.

Extraction electrodes 23 and 23' serving as signal lines are provided insuch a manner that the respective ends thereof are connected to thestarting points of windings of the coils 22 and 22' and that theelectrodes get over the coils 22 and 22' through insulation layers (notshown) and extend therefrom.

Also, as will be obvious from FIG. 4, the end points of windings of thecoils 22 and 22' are connected to extraction electrodes 24 and 24' whichare respectively formed at the locations near the side of the axis l ofsymmetry which passes through the center between the two coils.

In addition, yokes 25 and 25' constituting the upper magnetic layers areformed at the locations which extend from contact hole portions 28 and28' as the central portions of the respective coils to the sides of thesliding surfaces of the magnetic recording medium by getting over thecoils 22 and 22'. The edge portions of the yokes 25 and 25', namely, themagnetic pole portions sandwich magnetic gap materials together with thesubstrate 21 and form magnetic gaps 26 and 26' on the sides of slidingsurfaces of the magnetic recording medium.

In such a structure, by allowing currents to respectively flow among theextraction electrodes 23, 23' and 24, 24', the magnetic fields occur inthe coils 22 and 22', causing the magnetic fluxes in the magneticcircuits including the yokes 25 and 25' and the substrate 21. Themagnetic fields which project forwardly from the head gaps 26 and 26'are generated, so that it is possible to perform the magnetic recordingin accordance with the signal currents respectively supplied among theextraction electrodes 23, 23' and 24, 24'.

On the other hand, in case of reading the magnetically recorded signals,the magnetic fluxes caused from the side of the magnetic recordingmedium flow through the gaps 26 and 26' into the magnetic circuitsincluding the yokes 25 and 25' and the substrate 21. Thus, the voltagescorresponding to the changes in amounts of magnetic fluxes arerespectively developed among the extraction electrodes 23, 23' and 24,24' which are both ends of the coils 22 and 22', thereby allowing thesignals magnetically recorded to be reproduced.

In this way, the coils are symmetrically formed around the axis l ofsymmetry as a center on the substrate 21 with respect to the right andleft sides. The continuous extraction electrodes are arrangedsymmetrically with respect to the right and left sides from the startingpoints of windings of the coils and from the end points of windingsthereof. Due to this, the coils and electrode patterns are distributedat the same rates and this makes it possible to balance thecharacteristics between the two heads.

Therefore, there is no need to compensate the variation between theheads and perform the adjustment process, thereby enabling the crosstalkto be remarkably reduced.

FIG. 5 is a perspective view for explaining further another embodimentof the invention. This embodiment adopts the structure such thatadditional extraction electrodes 27 and 27' are provided in addition tothe extraction electrodes 23, 23', 24, and 24' shown in FIG. 4.

These extraction electrodes 27 and 27' serve as the common earth linesand the respective ends are connected to yokes 35 and 35' of therespective heads, while the other ends are extracted in parallel withthe extraction electrodes 23, 23', 24, and 24'.

With such a structure, the extraction electrodes 23, 23', 24, and 24'are shielded by the extraction electrodes 27 and 27' as the common earthlines arranged outside, so that an excellent shielding effect forexternal noises is obtained and the crosstalk can be further reduced.

In addition, by transmitting and receiving the signals through theextraction electrodes 23 and 23' sandwiched by the extraction electrodes27 and 27' as the common earth lines and the extraction electrodes 24and 24', the crosstalk at a high-frequency band is reduced and thetwo-channel thin-film magnetic heads which are hardly influenced by theexternal noises can be derived.

In the foregoing embodiments shown in FIGS. 4 and 5, examples using themagnetic substrates as the substrate 21 have been illustrated. However,it is also possible to adopt the structure such that a non-magneticsubstrate is used as the substrate 21 and the lower magnetic layer isindividually formed by a magnetic thin film on the non-magneticsubstrate.

According to the embodiments shown in FIGS. 4 and 5, it will beobviously understood from the above description that since they adoptthe structures such that the coils and extraction electrodes are formedon the substrate symmetrically with respect to the right and left sidesand that the extraction electrodes connected to the end points ofwindings of the coils are arranged at the locations near the side of theaxis of symmetry, the distributions of the coils and electrodes on theright and left sides are equal and the good high-frequency balancebetween the two heads is obtained, thereby enabling the crosstalk to beremarkably reduced, so that it is possible to obtain an excellent effectsuch that there is no need to perform the adjusting process tocompensate the variation between the right and left heads.

FIG. 6 is a perspective view showing thin-film magnetic heads accordingto still another embodiment of the invention, in which the same andsimilar parts and components as those shown in FIG. 4 are designated bythe same reference numerals.

In the diagram, the substrate 21 is made of magnetic material such asferrite or the like since it also serves as the lower magnetic layer asparts of the heads in this embodiment.

The coils 22 and 22' are adjacently formed on the substrate 21. However,as is obvious from the drawing, the end points of windings of the coils22 and 22' are respectively extracted from the outermost peripheries ofthe clockwise and counterclockwise windings and become the wireterminals (extraction electrodes) 24 and 24' which are used as the sidesof the common earth lines.

The upper magnetic layers 25 and 25' consisting of permalloy or the likeare led to the sides of the sliding surfaces of the recording medium ofthe substrate 21 from the contact holes 28 and 28' as the centralportions of the respective coils in the manner such that the layers 25and 25' get over the coils 22 and 22' through the insulation layers. Theupper magnetic layers 25 and 25' sandwich the head gap material togetherwith the substrate 21, thereby forming the head gaps 26 and 26'.

Also, the signal lines (extraction electrodes) 23 and 23' are arrangedinside the right and left wire terminals 24 and 24' such that they aresymmetrically located with regard to the axis l of symmetry.

The signal lines 23 and 23' are parallel to the wire terminals 24 and24' and the respective ends are connected to the contact holes 28 and28' at the centers of the coils 22 and 22' through the insulationlayers.

With such an arrangement, by allowing the currents to flow among thesignal lines 23, 23' and the wire terminals 24, 24' as the earth lines,the magnetic fields occur due to the coils 22 and 22' and the magneticfluxes flow through the magnetic circuits consisting of the uppermagnetic layers 25 and 25' and the substrate 21. Thus, the magneticfields protrude forwardly from the head gaps 26 and 26' and therecording is performed on the magnetic recording medium by thesemagnetic fields.

On the contrary, upon reproduction, the magnetic fluxes flowing into thehead gaps 26 and 26' from the recording medium flow through the magneticcircuits consisting of the substrate 21 and the upper magnetic layers 25and 25', so that the voltages corresponding to the changes in amounts ofmagnetic fluxes are developed among the signal lines 23, 23' and thewire terminals 24, 24' as both ends of the coils 22 and 22'. In thisway, the signals magnetically recorded are reproduced.

As described above, since the adjacent coils and signal lines and thelike are arranged symmetrically with respect to the right and leftsides, the mutual distributed capacities become equal, thereby enablingthe characteristics between the two heads to be balanced.

In addition, since the distance between the signal lines 23 and 23' iswider than the distance between the respective wire terminals 24 and24', the crosstalk between the heads is reduced, causing a shieldingeffect since the external noises are shut off due to the existance ofthe wire terminals 24 and 24'.

FIG. 7 is a diagram for explaining further another embodiment of theinvention, in which the same and corresponding parts and components asthose shown in FIG. 6 are designated by the same reference numerals andtheir descriptions are omitted.

This embodiment adopts the structure such that a common earth line 37 isindividually provided at the center of the right and left head portionsand it is connected to the upper magnetic layers 35 and 35'.

With such a structure, since the signal lines 23 and 23' arerespectively shielded by the common earth line 37, the crosstalk isfurther reduced as compared with the embodiment shown in FIG. 6.

In the two embodiments shown in FIGS. 6 and 7, examples whereby thesubstrate 21 constitutes the lower magnetic layer have been illustrated.However, the above-described structure can be also similarly applied tothe magnetic heads of the types whereby the substrate 21 is made ofnon-magnetic material and the lower magnetic layer is individuallyformed thereon.

As is obvious from the above description, according to the embodimentsshown in FIGS. 6 and 7, since they adopt the structures whereby thecoils formed on the substrate are line-symmetrically arranged and thewire terminals led out from the respective coils are arranged outsideand signal lines are arranged inside the respective wire terminals, thedistributed capacities of the two head sections become equal and goodhigh-frequency balance is obtained, so that the crosstalk is extremelyreduced.

On the other hand, by forming the common earth line between the rightand left signal lines, the respective signal lines are shielded by thecommon earth lines, thereby enabling the crosstalk to be furtherreduced.

In addition, since the extraction lines from the coils are located atthe outermost positions, this also presents a shielding effect ofreduction of the external noises, so that the stable operations of themagnetic heads can be performed.

What we claim is:
 1. A thin film magnetic head for simultaneouslytracing two tracks, comprising:a substrate; and a pair of yokes eachbeing disposed on said substrate and formed by a magnetic thin film,each yoke having a magnetic pole portion and an expanded portionthereof, wherein each magnetic pole portion is spaced from saidsubstrate to form a magnetic gap disposed between said substrate andeach magnetic pole portion, and wherein the cross sectional area of eachexpanded portion taken through a plane perpendicular to the top surfaceof said expanded portion is larger than the cross sectional area of saidmagnetic pole portion taken through a plane perpendicular to the topsurface of said magnetic pole portion, and wherein the distance betweensaid pair of expanded portions increases as the distance from saidmagnetic pole portions increases.
 2. A thin film magnetic head accordingto claim 1, wherein said pair of yokes are symmetrical with respect to aline.
 3. A thin film magnetic head according to claim 2, wherein thelateral edge of each magnetic pole portion is rectilinear.
 4. A thinfilm magnetic head according to claim 3, wherein the lateral edge ofeach expanded portion has an arc-like shape.